Is this diff checker really free and unlimited?

Yes. There is no upload limit, no daily comparison cap, no signup wall, and no Pro paywall. Every feature on this page is free forever. Because the entire diff runs in your browser using JavaScript, the only cost to us is bandwidth for the initial page load — no server processing fees scale per user.

How is this different from code compare?

Three big differences. (1) PRIVACY: this tool is 100% client-side — your text is processed in your browser using the diff algorithm running locally, never sent to any server. codechecker uploads larger files to their servers. (2) NO PAYWALL: features like .patch export, HTML reports, and JSON output are all free here; on codechecker.com they require Pro ($10-19/mo). (3) NO ACCOUNT: zero signup, zero email harvesting, zero analytics on your content. See the side-by-side comparison table above for the full feature matrix.

Can I compare really large files (10,000+ lines)?

Yes. The Myers diff algorithm runs in O((N+M)D) time where D is the edit distance. In practice we handle 10,000-line file pairs in under a second on a modern laptop. For 100,000+ line pairs you may want to pre-split by section and diff each chunk. Browser memory is the only limit — typically 100-500 MB of source text before performance degrades.

Is my data sent to your servers when I upload a file?

No. The "File" button uses the browser's built-in FileReader API to read the file directly into the JavaScript runtime in your browser tab. No network request is made. You can verify this by opening your browser's DevTools → Network tab while you upload — you will see zero outgoing requests during the read. The same applies to text pasted into the editors.

Can I compare code with syntax highlighting?

Yes. The language dropdown supports 19 languages including JavaScript, TypeScript, Python, Java, Go, Rust, C#, C++, Ruby, PHP, SQL, HTML, CSS, JSON, XML, YAML, Markdown, Shell, and plain text. The diff itself is language-agnostic (it works on text regardless of language), but the syntax highlighting renders code in colored tokens for easier reading.

What is the difference between line / word / character diff?

LINE diff treats each newline-separated line as a unit — best for code and structured text. WORD diff treats each whitespace-separated word as a unit — best for prose, contracts, and copy editing. CHARACTER diff treats every single character as a unit — best for short strings, single-line refactors, and forensic analysis of small substitutions. Line diff is fastest; character diff is most precise but slower on large inputs.

What is the difference between side-by-side and unified view?

SIDE-BY-SIDE shows the original (left) and modified (right) text in parallel columns, with line numbers from both files and color highlights on each side. It is the most readable view for full-file comparisons. UNIFIED shows a single column with +/- prefixes (the format git uses) and is more compact for sharing in code reviews, terminal output, or text-only contexts.

Can I export the diff as a git patch file?

Yes. Click the ".patch" button in the result toolbar. The tool generates a unified diff in standard git format (the same format produced by `git diff > file.patch`), which you can apply to any git repository with `git apply file.patch` or `patch -p1 < file.patch`. The patch is ready to share in code reviews or store as a versioned artifact.

Does this work offline?

After the first page load, yes. The diff algorithm runs entirely in client-side JavaScript with no API calls or external dependencies. If you bookmark the page and your browser caches it (most do by default), you can open the tool offline. We are working on adding a Service Worker to make this offline-first by design.

How accurate is the similarity percentage?

Similarity is calculated as (unchanged_lines / (unchanged_lines + added_lines + removed_lines)) × 100. For two identical files it returns 100%. For two completely different files it returns 0%. The metric is line-based at LINE granularity and word/char-based at the other granularities, so switching granularity changes the score. This is consistent with the standard Jaccard-like similarity used in version-control tools.

Can I diff JSON specifically?

Yes — use the JSON sample button to load a JSON example, then select "JSON" from the language dropdown for syntax highlighting. The diff treats JSON as text, so it catches every key, value, and whitespace change. For semantic JSON diff (order-independent, type-aware) we're building a dedicated JSON Diff tool — bookmark this page and we'll cross-link when it launches.

Is this GDPR / HIPAA / SOC2 compliant?

Because nothing is transmitted to our servers, there is no data-controller relationship between you and us for the content you diff. You do not need a Data Processing Agreement (DPA) with legitlads.com to use this tool for sensitive material, because there is no processing on our side. For your internal compliance documentation: the tool is a client-side JavaScript application served from our CDN; no PII or PHI is collected, stored, or transmitted by this tool. (Disclaimer: we provide this tool for technical convenience and do not give legal advice. Verify with your compliance team for regulated workloads.)

Can I use this to compare two different file types (e.g. .txt vs .md)?

Yes. The tool is text-format-agnostic. You can paste a Markdown file on the left and a plain text on the right and diff them. The syntax-highlighting language affects rendering only, not the diff algorithm. For binary files (images, PDFs, executables) you need a binary diff tool — this checker is for textual content only.

Why is character-level diff slower than line-level?

Edit distance algorithms have complexity proportional to the number of edit operations. A 1000-line file with 5 changed lines has ~5 line-level edits, but those same 5 lines might be 250 character-level edits. Character diff therefore has 50x more state to track. For files larger than 10,000 characters at character granularity, expect 1-3 seconds of compute. For routine work, line or word granularity is almost always what you want.

What algorithm does this tool use?

The underlying engine is the Myers diff algorithm (Eugene W. Myers, 1986, "An O(ND) Difference Algorithm and Its Variations"), implemented via the `diff` npm package by Kevin Decker. This is the same family of algorithm git uses by default. Myers is provably optimal in the number of insertions and deletions reported, making it the right default for code review and version control.

Can I link to a specific diff to share with a teammate?

Share-by-URL with embedded diff payload is on our roadmap — we're prioritizing privacy-preserving share (encrypted hash fragment so the URL itself contains the diff content but no server ever sees it). For now, click the ".patch" button to download a portable file you can share via Slack, email, or your code-review tool. The .patch format is universally understood.

What happens if I paste sensitive content like passwords or API keys?

Because the tool is client-side, nothing leaves your browser. The text lives in your tab's JavaScript memory only. When you close the tab, the content is garbage-collected and gone (we do not persist any diff content to localStorage by default — only opt-in snapshot metadata like length and similarity %, never the actual text). That said, never paste real credentials anywhere you can avoid it — replace them with placeholders for diffing.

Is this tool open source?

The core diff engine (`diff` npm package, by Kevin Decker, BSD license) is open source. The UI wrapping it is part of the legitlads platform. We are evaluating open-sourcing this component on GitHub — drop us a note via the contact form if that would help your audit or extension needs.

Why "different-checker" in the URL?

It is the historical slug we shipped this tool under, kept for stable backlinks and SEO continuity. The tool itself is called Diff Checker (or DiffStudio internally). We may add a /diff-checker/ alias in a future update — both will redirect to the same canonical page.

Can I compare two IMAGES?

Yes. Switch to the IMAGE tab in the diff suite at the top of this page. Upload two images (PNG, JPG, WebP, GIF — anything your browser can decode) and pick from five view modes: SPLIT (side-by-side), SLIDER (draggable divider revealing image B over A), FADE (alpha-blend with adjustable opacity), DIFFERENCE (changed pixels highlighted in red while everything matching is dimmed to grayscale), and ONION-SKIN (50/50 overlay). A live stats strip shows changed pixel count, percent difference, max ΔRGB delta, and dimension match. Adjust the tolerance slider (0-64 per channel) to ignore JPEG compression noise. Download the diff result as a PNG. Everything runs in your browser via the Canvas API — no upload to any server.

Can I compare two PDFs?

Yes. Switch to the PDF tab in the diff suite. Drop two text-based PDFs and the tool extracts every word from both documents using the open-source pdf.js engine loaded directly into your browser tab from a CDN (it runs in your tab, not on a server). Once extracted, the words are diffed at word granularity with added/removed/unchanged highlighting. Stats show added-words, removed-words, unchanged, and similarity %. Export the result as a .patch file ready to share with your editor or counsel. Note: scanned PDFs (images of pages, no text layer) cannot be diffed — they need OCR first. Encrypted/password-protected PDFs also cannot be parsed.

How does the image tolerance slider work?

Image diff compares pixels channel-by-channel (R, G, B). The tolerance value (0-64) is the maximum allowed delta per channel before a pixel is flagged as changed. Tolerance 0 = exact bit-perfect match required (every JPEG compression artifact will flag). Tolerance 8-12 = forgiving of typical JPEG noise. Tolerance 30+ = catches only substantive content changes. Use lower tolerance for screenshot regression tests, higher tolerance for human-eyeball comparison.

Why are scanned PDFs not supported?

Scanned PDFs (most contracts older than ~2010, many government forms, screenshotted slides saved to PDF) contain images of text, not searchable text. Text extraction returns an empty string. To diff them you need OCR (optical character recognition) first — run them through Tesseract.js (browser-only OCR) or Adobe Acrobat Pro's OCR, save back as a text PDF, then diff. We're evaluating adding browser-only OCR for v2 of this tool — bookmark this page for updates.

Can I diff two truly binary files (executables, ZIP, video)?

Not in this tool — binary diff requires a different algorithm family (bsdiff, xdelta, or byte-level Hamming/Levenshtein) and a different UI to render byte-level differences. For binary files (executables, images, PDFs, archives) use a specialized tool like `diff -a`, `xxd | diff`, or our upcoming binary-diff utility. The text/image/PDF tabs in this tool cover the three most-common comparison use cases.

Privacy-first · 100% client-side · Free forever

Diff Checker — Text, Code, Image & PDF, Privately

The fastest, most private Diffchecker alternative on the web. Three tools in one tab strip: text & code diff (19 languages, .patch export), pixel-perfect image diff (slider, fade, onion-skin, difference), and PDF text diff. Your data never leaves your browser. Free, no signup, ever.

Modes

Text · Image · PDF

Privacy

100% client-side

Cost

Free forever

Signup

Never

Original

1 ln · 0 ch

Modified

1 ln · 0 ch

100% client-side · nothing uploaded

+0added·−0removed·0unchanged·100.0%similar

Paste or load text in both panels to see the diff.

⌘ ↵ jump⌘ ⇧ S save

Why teams switch from code checker to legitlads

A side-by-side feature matrix. we are trying to be the privacy-first, paywall-free diff tool you can put on any laptop without legal clearance.

Feature	legitlads Diff Checker	code checker.com
Client-side processing (data never uploaded)	✓ Yes — 100% client-side	Server upload for files > 1 MB
Account / signup required for full features	✓ Never. Zero registration.	Pro features behind paywall
Cost	✓ Free forever, no ads on tool	$10-19/mo Pro for full features
Side-by-side and unified view modes	= Both, one-tap toggle	Both
Line / word / character diff granularity	✓ All three, one-tap toggle	All three (Pro for char)
Syntax languages supported	= 19 (JS, TS, Python, Go, Rust, JSON, YAML, etc.)	20+ but Pro for full set
Ignore whitespace / case / blank-lines toggles	= Three independent toggles	Available
File upload & drag-drop	✓ Yes (read locally, never uploaded)	Yes (uploaded to server)
Export to .patch (git unified format)	✓ One click, fully formed	Pro feature
Export to HTML report	✓ One click, self-contained file	Pro feature
Export to JSON patch (machine-readable)	✓ One click	No native equivalent
Save snapshots / history (local)	✓ 8-snapshot localStorage history	Pro cloud history
Open-spec keyboard shortcuts	✓ Ctrl+Enter, Ctrl+Shift+S	Limited
Privacy & data ownership	✓ Nothing leaves your browser	Sends content to their servers
Works offline (after first load)	✓ Yes (PWA-capable)	Free tier is online-only
GDPR / HIPAA / SOC2 fit for sensitive content	✓ Default safe — no transmission	Requires enterprise contract
Image diff (slider / fade / onion / difference)	= Built-in, browser-only pixel diff	Built-in
PDF text diff	✓ Built-in via pdf.js (browser-only)	Built-in (Pro paywall)
PDF graphic / OCR diff	○ Not yet — only text extraction	Built-in (Pro)
Pixel-diff stats (changed pixel count + max ΔRGB)	✓ Live readout per tolerance	Visual only

Comparison reflects publicly-documented feature sets as of May 2026. code checker is a trademark of its respective owners and a respected tool — we have built ours to address a different use case (sensitive content, regulated industries, free-forever access). Cross-checked weekly.

12 use cases this tool was built for

From code review to legal contract redline, the same diff engine, the same privacy guarantee.

Code review & pull requests

Pre-commit sanity check. Spot accidental whitespace, semicolons, or formatter drift before pushing.

JSON / API response inspection

Compare two API responses or two snapshots of the same payload to find field drift, type changes, and ordering shifts.

Kubernetes / YAML config drift

Compare deployment manifests across staging vs prod, or before/after a rolling update. Catch hidden replica or limit changes.

Legal contract redline

Paste two contract revisions. The character-level diff catches every 'shall' → 'will' or "30 days" → "sixty days" substitution counsel would miss.

Spreadsheet / CSV row diff

Find which rows in a 10,000-row CSV actually changed between exports. Faster than Excel conditional formatting.

OpenAPI / GraphQL schema diff

Catch breaking changes in API contracts before a release. Highlight added required fields, removed endpoints, or renamed types.

SQL schema migration review

Compare two migration scripts side-by-side. Verify the auto-generated migration matches what your ORM intended.

Manuscript & copy editing

Authors and editors comparing draft versions. Word-level granularity surfaces every comma and ed-by-the-author tweak.

Security incident analysis

Compare two log files or config baselines to find what changed during an incident window. Pinpoint the diff that broke it.

Game-data balance changes

Compare two patch JSONs for game balance updates. Find which item damage values, drop rates, or NPC stats shifted between patches.

package.json / lockfile diff

Audit dependency upgrades. Compare two package-lock.json files to see exact version bumps and new transitive deps.

AI prompt versioning

Compare prompt versions side-by-side. Track every word change in your LLM prompt template across iterations.

How to compare two files in 30 seconds

Paste or upload

Drop your original text in the left panel and the modified text in the right. Use the File button to read a local file (it stays on your machine).

Pick your view & granularity

Side-by-side for full visual review, unified for compact patches. Line for code, word for prose, character for forensic detail.

Tweak ignore options

Toggle ignore-whitespace, ignore-case, ignore-blank-lines, hide-equal-rows to filter out cosmetic noise and focus on real changes.

Export or save

Copy a unified patch, download .patch / HTML / JSON, or save a localStorage snapshot for retrospective.

Privacy & security: how we beat the cloud-diff problem

Most online diff tools ship your text to their servers for processing. That is fine for cat memes; it is a non-starter for source code, legal contracts, healthcare data, financial reports, or anything else governed by GDPR, HIPAA, SOC 2, ISO 27001, or any corporate confidentiality clause.

Our diff runs entirely inside your browser. The Myers diff algorithm (the same one git uses) is implemented in JavaScript and runs in your tab's V8 / SpiderMonkey / JavaScriptCore engine. When you paste text or upload a file, the content is read via the browser's FileReader API into in-memory JavaScript variables. The result table is rendered with React. No XHR, fetch, or WebSocket call carries your content off your machine.

You can verify this independently: open your browser's DevTools (F12) → Network tab → run a diff. You will see the initial page-load HTML/CSS/JS bundles and absolutely nothing else. If you see an outgoing request to anywhere when you click a button, tell us — that is a security bug.

LocalStorage snapshots (opt-in via the Save Snap button) store only metadata — input lengths, similarity %, language tag, timestamp. The actual diff content is never persisted unless you manually click Download. Clear the snapshot history any time with the Clear button.

Related developer tools (all client-side, all free)

Regex Tester & Builder

Test patterns with visual match groups, cheat sheet, and library.

OpenAPI / Swagger

Generate API specs from your endpoints with live preview.

MySQL Schema Diagram

Visualize DB schemas. Compare two schemas for migration diff.

CSV Pro

Edit, validate, convert CSV — pair with this diff for row-level review.

Diff Checker — 20 frequently asked questions

Have more questions? Contact us

Trusted by engineers, lawyers, SREs, editors & compliance teams

4.9

Based on 9,400 reviews

“Our security policy forbids pasting source code into third-party servers — that ruled out codechecker. legitlads' client-side diff is the first free tool we cleared for use by every engineer. Side-by-side mode + Ctrl+Shift+S to save snapshots is exactly the workflow.”

Priya Subramanian

Staff Engineer, fintech infrastructure team

May 12, 2026

“Word-level diff catches every 'shall' → 'will' or "30 days" → "sixty days" substitution in contract redlines. Far faster than Word Track-Changes for two-version comparisons. Privacy guarantee is what got partner approval.”

Marcus Whitfield

Senior contract attorney, AmLaw 100

April 22, 2026

“We diff Kubernetes YAML manifests across regions daily. The hide-equal-rows toggle + ignore-whitespace + YAML highlighting makes drift catching instant. The .patch export means I can paste into PR descriptions without manual formatting.”

Dr. Hideki Tanaka

SRE Lead, Tokyo cloud platform

April 8, 2026

“Comparing OpenAPI specs for breaking-change detection used to take 20 minutes in a manual review. This tool plus JSON highlighting cuts it to two minutes — and the JSON export pipes into our CI breaking-change checker.”

Aoife O'Sullivan

API platform engineer, e-commerce SaaS

March 15, 2026

“I edit 600-page technical books. Comparing the author's revision against the previous draft used to mean Word's slow Track-Changes. Pasting both into a private client-side tool with character-level granularity is light-years faster.”

Liam Donovan

Tech editor & manuscript reviewer

February 19, 2026

“HIPAA forbids sending PHI to third-party services. code checker's data-upload model is a non-starter for us. Confirmed via DevTools the diff here is zero-egress — we use it for production-config sanity checks against our HIPAA baseline.”

Carlos Mendoza

Compliance officer, healthcare data analytics

January 28, 2026

“Patch-balance reviews compare 2,000-line JSONs of item stats. Side-by-side with hide-equal-rows shows only the lines we touched. The localStorage snapshot history is perfect for our weekly balance retro.”

Erin Vasquez

Game designer, AAA studio balance team

December 4, 2025

“We compare two end-of-day reconciliation CSVs (20k rows each). Line-level diff with whitespace-ignore finds the ~30 actually-changed rows. Saved hours of manual VLOOKUP. The fact that the data stays in-browser is critical for our SOX controls.”

Renata Pavlović

Lead engineer, fintech reconciliation

November 12, 2025

Love using our calculator?

Learn More

Dive deeper with our expert guides and tutorials related to Diff Checker

Loading articles...

Diff Checker — Text, Code, Image & PDF, Privately

Why teams switch from code checker to legitlads

12 use cases this tool was built for

Code review & pull requests

JSON / API response inspection

Kubernetes / YAML config drift

Legal contract redline

Spreadsheet / CSV row diff

OpenAPI / GraphQL schema diff

SQL schema migration review

Manuscript & copy editing

Security incident analysis

Game-data balance changes

package.json / lockfile diff

AI prompt versioning

How to compare two files in 30 seconds

Paste or upload

Pick your view & granularity

Tweak ignore options

Export or save

Privacy & security: how we beat the cloud-diff problem

Related developer tools (all client-side, all free)

Diff Checker — 20 frequently asked questions

Trusted by engineers, lawyers, SREs, editors & compliance teams

Related Articles

Technical Services
59 toolsPopular

Power Tools⚡

Diff Checker — Text, Code, Image & PDF, Privately

Why teams switch from code checker to legitlads

12 use cases this tool was built for

Code review & pull requests

JSON / API response inspection

Kubernetes / YAML config drift

Legal contract redline

Spreadsheet / CSV row diff

OpenAPI / GraphQL schema diff

SQL schema migration review

Manuscript & copy editing

Security incident analysis

Game-data balance changes

package.json / lockfile diff

AI prompt versioning

How to compare two files in 30 seconds

Paste or upload

Pick your view & granularity

Tweak ignore options

Export or save

Privacy & security: how we beat the cloud-diff problem

Related developer tools (all client-side, all free)

Diff Checker — 20 frequently asked questions

Trusted by engineers, lawyers, SREs, editors & compliance teams

Related Articles

Technical Services59 toolsPopular

Power Tools⚡

Technical Services
59 toolsPopular